Bernie Sanders won decisive victories in Democratic caucuses in Alaska, Washington and Hawaii Saturday, giving his campaign a much-needed boost as he seeks to disrupt Hillary Clinton's path to the party's presidential nomination.

While the results barely dented Hillary Clinton’s significant delegate lead, Sanders’ wins underscored her persistent vulnerabilities within her own party, particularly with young voters and liberal activists who have been inspired by her rival’s unapologetically liberal message.

There are 22 more Democrat primaries to go before June 14.

Sanders cast his performance as part of a Western comeback, telling the Associated Press that he expects to close the delegate gap with Clinton as the contest moves to the more liberal northeastern states, including her home state of New York. He also said his campaign is increasing its outreach to superdelegates, the party insiders who can pick either candidate, and are overwhelmingly with Clinton.

“The Deep South is a very conservative part of the country,” Sanders said. “Now that we’re heading into a progressive part of the country, we expect to do much better.”

He added: “There is a path to victory.” With Clinton far in front, however, it is a difficult path.

Clinton anticipated Saturday’s losses against the Vermont senator: She barely campaigned in the three states, making just one day of stops in Washington state, and was spending the Easter weekend with her family.

US networks projected Sanders winning by wide margins in all three states where 142 delegates were up for grabs – 101 in Washington, 16 in Alaska and 25 in Hawaii.

The networks projected Sanders winning 79 percent against 21 percent for Clinton in Alaska. In Washington, he was projected to win 72 percent against 28 for Clinton. In Hawaii 71 percent against Clinton’s 29 percent.

Going into Saturday, Clinton had already amassed 1,711 delegates, including superdelegates who are unelected by voters, compared to 952 for Sanders, according to a CNN count.

To win the Democratic nomination at the July convention in Philadelphia, 2,383 delegates are needed.

Uphill battle

Despite his victories on Saturday, Sanders, who has drawn strong support from young voters with his populist message, still faces an uphill battle to overcome Clinton's lead, especially as Democrats allocate delegates proportionally by state.

Sanders spent millions of dollars on campaign ads ahead of Saturday's caucuses and visited Seattle on Friday, giving a rousing rendition of his standard stump speech in which he railed against police brutality, a too-low minimum wage, soaring student debt and other ills.

"Real change historically always takes place from the bottom on up when millions of people come together," Sanders said to applause and cheers from the crowd in the city's Safeco Field baseball stadium.

"We need a political revolution!"

He repeated that same message on Saturday in Wisconsin – the next state to hold primaries on April 5 – and reiterated his vow to legalise marijuana.

"Everybody knows marijuana is not a killer drug like heroin," he said. "And that is why I have introduced legislation to take marijuana out of the controlled substance act."

By contrast, Clinton in recent days has already shifted her focus toward November's general election.

She delivered a somber counterterrorism speech Wednesday in the aftermath of deadly attacks in Brussels, using it as an opportunity to launch vigorous assaults on Republican candidates Donald Trump and Ted Cruz and warn their "reckless" foreign policies would harm US interests.

"We need to rely on what actually works, not bluster that alienates our partners and doesn't make us any safer," she said.

Despite the huge delegate gap with Clinton that he needs to fill, Sanders has refused to throw in the towel.

A series of recent polls has shown Sanders consistently doing better than Clinton against Republicans Trump, Cruz and Ohio Governor John Kasich.

Saturday's three contests were caucuses, essentially neighborhood meetings where voters can discuss political platforms and debate the merits of the candidates.

Since they generally require voters to show up in person rather than mailing primary ballots, the format favours Sanders, whose supporters have consistently shown more grassroots enthusiasm.

Millennials and first-time voters have been flocking to Sanders's message of economic equality, universal health care and his call to reduce the influence of billionaires on the campaign finance system.

But the delegate math still dramatically favours Clinton.

According to RealClearPolitics poll averages, in the remaining states with the three largest delegate allocations – California, New York and Pennsylvania – Clinton leads Sanders by nine points, 34 points and 28 points respectively.